(This chapter has been reprinted with permission from Williams MV, Hayward R: Comprehensive Hospital Medicine, 1st edition. Philadelphia, WB Saunders, in press.)
Nosocomial pneumonia (NP) is the leading cause of mortality among patients who die from hospital-acquired infections. Defined as pneumonia occurring 48 hours or more after hospital admission, NP also includes the subset of ventilator-associated pneumonia (VAP), defined as pneumonia developing 48 to 72 hours after initiation of mechanical ventilation. The incidence of NP is between 5 and 15 cases per 1000 hospital admissions. Healthcare-associated pneumonia (HCAP), part of the continuum of NP, describes an increasingly common proportion of pneumonia developing outside the hospital (Table I) (1). Typically afflicting people in a nursing home or assisted living setting, these patients are at risk for antibiotic-resistant-organisms and should be approached similarly to cases of nosocomial pneumonia rather than community-acquired pneumonia. Most of the data informing our diagnostic and treatment decisions about NP come from studies performed in mechanically ventilated patients and are extrapolated to make recommendations for non-ventilated patients.
Mortality attributable to NP is debated, but may be as high as 30%. The presence of nosocomial pneumonia increases hospital length of stay an average of 7–10 days, and in the case of VAP, is estimated to cost between $10,000 and $40,000 per case (2).
Signs and Symptoms
Nosocomial pneumonia is usually diagnosed based on clinical grounds. Typical symptoms and signs consist of fever, cough with sputum, and shortness of breath in the setting of hypoxia and a new infiltrate on chest radiograph (CXR). In the elderly, signs may be more subtle and delirium, fever, or leukocytosis in the absence of cough should trigger its consideration. The likelihood of NP increases among patients with risk factors for microaspiration, oropharyngeal colonization, or overgrowth of resistant organisms (Table II) (3).
Prior to settling on a diagnosis of NP, alternative causes of fever, hypoxia, and pulmonary infiltrates should be considered. Most commonly, these include pulmonary embolus, pulmonary edema, or atelectasis. Alternative infectious sources, such as urinary tract, skin and soft-tissue infections, and device-related infections (i.e., central venous catheters) are common in hospitalized patients and should be ruled out before diagnosing nosocomial pneumonia.
Diagnostic strategies for NP seek to confirm the diagnosis and identify an etiologic pathogen, thus allowing timely, effective, and streamlined antibiotic therapy. Unfortunately, no consensus exists on the best approach to diagnosing nosocomial pneumonia. After obtaining a complete blood count and blood cultures, you can choose between a clinical or microbiologic diagnostic approach to diagnosis. A clinical diagnosis relies on a new or progressive radiographic infiltrate along with signs of infection such as fever, leukocytosis, or purulent sputum. Clinical diagnosis is sensitive, but is likely to lead to antibiotic overuse. The microbiologic approach requires sampling of secretions from the respiratory tract and may reduce inappropriate antibiotic use, but takes longer and may not be available in all hospitals.